Java tutorial
package co.tinode.tindroid; /* * Copyright (C) 2013 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ import android.content.Context; import android.content.res.Resources; import android.graphics.Bitmap; import android.graphics.BitmapFactory; import android.graphics.drawable.BitmapDrawable; import android.graphics.drawable.ColorDrawable; import android.graphics.drawable.Drawable; import android.graphics.drawable.TransitionDrawable; import android.os.AsyncTask; import android.os.Bundle; import android.support.v4.app.Fragment; import android.support.v4.app.FragmentManager; import android.support.v4.util.LruCache; import android.util.Log; import android.widget.ImageView; import java.io.FileDescriptor; import java.lang.ref.WeakReference; /** * This class wraps up completing some arbitrary long running work when loading a bitmap to an * ImageView. It handles things like using a memory and disk cache, running the work in a background * thread and setting a placeholder image. */ public abstract class ImageLoader { private static final String TAG = "ImageLoader"; private static final float MEMORY_PERCENT = 0.1f; private Bitmap mLoadingBitmap; private boolean mPauseWork = false; private final Object mPauseWorkLock = new Object(); private int mImageSize; private Resources mResources; private LruCache<String, Bitmap> mBitmapCache; protected ImageLoader(Context context, int imageSize, FragmentManager fm) { mResources = context.getResources(); mImageSize = imageSize; final RetainFragment mRetainFragment = findOrCreateRetainFragment(fm); // See if we already have an ImageCache stored in RetainFragment mBitmapCache = (LruCache<String, Bitmap>) mRetainFragment.getObject(); // No existing ImageCache, create one and store it in RetainFragment if (mBitmapCache == null) { int maxSize = Math.round(MEMORY_PERCENT * Runtime.getRuntime().maxMemory() / 1024); mBitmapCache = new LruCache<String, Bitmap>(maxSize) { /** * Measure item size in kilobytes rather than units which is more practical * for a bitmap cache */ @Override protected int sizeOf(String key, Bitmap bitmap) { final int bitmapSize = bitmap.getByteCount() / 1024; return bitmapSize == 0 ? 1 : bitmapSize; } }; mRetainFragment.saveObject(mBitmapCache); } } public int getImageSize() { return mImageSize; } /** * Load an image specified by the data parameter into an ImageView (override * {@link ImageLoader#processBitmap(Object)} to define the processing logic). If the image is * found in the memory cache, it is set immediately, otherwise an {@link AsyncTask} will be * created to asynchronously load the bitmap. * * @param data The URL of the image to download. * @param imageView The ImageView to bind the downloaded image to. */ public void loadImage(Object data, ImageView imageView) { if (data == null) { return; } Bitmap bitmap = getBitmapFromCache(String.valueOf(data)); if (bitmap != null) { // Bitmap found in memory cache imageView.setImageDrawable(new RoundedImage(bitmap)); } else if (cancelPotentialWork(data, imageView)) { final BitmapWorkerTask task = new BitmapWorkerTask(imageView); final AsyncDrawable asyncDrawable = new AsyncDrawable(mResources, mLoadingBitmap, task); imageView.setImageDrawable(asyncDrawable); task.execute(data); } } /** * Set placeholder bitmap that shows when the the background thread is running. * * @param resId Resource ID of loading image. */ public void setLoadingImage(int resId) { mLoadingBitmap = BitmapFactory.decodeResource(mResources, resId); } /** * Subclasses should override this to define any processing or work that must happen to produce * the final bitmap. This will be executed in a background thread and be long running. For * example, you could resize a large bitmap here, or pull down an image from the network. * * @param data The data to identify which image to process, as provided by * {@link ImageLoader#loadImage(Object, ImageView)} * @return The processed bitmap */ protected abstract Bitmap processBitmap(Object data); /** * Cancels any pending work attached to the provided ImageView. */ public static void cancelWork(ImageView imageView) { final BitmapWorkerTask bitmapWorkerTask = getBitmapWorkerTask(imageView); if (bitmapWorkerTask != null) { bitmapWorkerTask.cancel(true); if (BuildConfig.DEBUG) { final Object bitmapData = bitmapWorkerTask.data; Log.d(TAG, "cancelWork - cancelled work for " + bitmapData); } } } /** * Returns true if the current work has been canceled or if there was no work in * progress on this image view. * Returns false if the work in progress deals with the same data. The work is not * stopped in that case. */ public static boolean cancelPotentialWork(Object data, ImageView imageView) { final BitmapWorkerTask bitmapWorkerTask = getBitmapWorkerTask(imageView); if (bitmapWorkerTask != null) { final Object bitmapData = bitmapWorkerTask.data; if (bitmapData == null || !bitmapData.equals(data)) { bitmapWorkerTask.cancel(true); if (BuildConfig.DEBUG) { Log.d(TAG, "cancelPotentialWork - cancelled work for " + data); } } else { // The same work is already in progress. return false; } } return true; } /** * @param imageView Any imageView * @return Retrieve the currently active work task (if any) associated with this imageView. * null if there is no such task. */ private static BitmapWorkerTask getBitmapWorkerTask(ImageView imageView) { if (imageView != null) { final Drawable drawable = imageView.getDrawable(); if (drawable instanceof AsyncDrawable) { final AsyncDrawable asyncDrawable = (AsyncDrawable) drawable; return asyncDrawable.getBitmapWorkerTask(); } } return null; } /** * The actual AsyncTask that will asynchronously process the image. */ private class BitmapWorkerTask extends AsyncTask<Object, Void, Bitmap> { private Object data; private final WeakReference<ImageView> imageViewReference; public BitmapWorkerTask(ImageView imageView) { imageViewReference = new WeakReference<ImageView>(imageView); } /** * Background processing. */ @Override protected Bitmap doInBackground(Object... params) { data = params[0]; final String dataString = String.valueOf(data); Bitmap bitmap = null; // Wait here if work is paused and the task is not cancelled synchronized (mPauseWorkLock) { while (mPauseWork && !isCancelled()) { try { mPauseWorkLock.wait(); } catch (InterruptedException ignored) { } } } // If the task has not been cancelled by another thread and the ImageView that was // originally bound to this task is still bound back to this task and our "exit early" // flag is not set, then call the main process method (as implemented by a subclass) if (!isCancelled() && getAttachedImageView() != null) { bitmap = processBitmap(params[0]); } // If the bitmap was processed and the image cache is available, then add the processed // bitmap to the cache for future use. Note we don't check if the task was cancelled // here, if it was, and the thread is still running, we may as well add the processed // bitmap to our cache as it might be used again in the future if (bitmap != null) { addBitmapToCache(dataString, bitmap); } return bitmap; } /** * Once the image is processed, associates it to the imageView */ @Override protected void onPostExecute(Bitmap bitmap) { // if cancel was called on this task or the "exit early" flag is set then we're done if (isCancelled()) { bitmap = null; } final ImageView imageView = getAttachedImageView(); if (bitmap != null && imageView != null) { imageView.setImageDrawable(new RoundedImage(bitmap)); } } @Override protected void onCancelled(Bitmap bitmap) { super.onCancelled(bitmap); synchronized (mPauseWorkLock) { mPauseWorkLock.notifyAll(); } } /** * Returns the ImageView associated with this task as long as the ImageView's task still * points to this task as well. Returns null otherwise. */ private ImageView getAttachedImageView() { final ImageView imageView = imageViewReference.get(); final BitmapWorkerTask bitmapWorkerTask = getBitmapWorkerTask(imageView); if (this == bitmapWorkerTask) { return imageView; } return null; } } /** * A custom Drawable that will be attached to the imageView while the work is in progress. * Contains a reference to the actual worker task, so that it can be stopped if a new binding is * required, and makes sure that only the last started worker process can bind its result, * independently of the finish order. */ private static class AsyncDrawable extends BitmapDrawable { private final WeakReference<BitmapWorkerTask> bitmapWorkerTaskReference; public AsyncDrawable(Resources res, Bitmap bitmap, BitmapWorkerTask bitmapWorkerTask) { super(res, bitmap); bitmapWorkerTaskReference = new WeakReference<>(bitmapWorkerTask); } public BitmapWorkerTask getBitmapWorkerTask() { return bitmapWorkerTaskReference.get(); } } /** * Pause any ongoing background work. This can be used as a temporary * measure to improve performance. For example background work could * be paused when a ListView or GridView is being scrolled using a * {@link android.widget.AbsListView.OnScrollListener} to keep * scrolling smooth. * <p> * If work is paused, be sure setPauseWork(false) is called again * before your fragment or activity is destroyed (for example during * {@link android.app.Activity#onPause()}), or there is a risk the * background thread will never finish. */ public void setPauseWork(boolean pauseWork) { synchronized (mPauseWorkLock) { mPauseWork = pauseWork; if (!mPauseWork) { mPauseWorkLock.notifyAll(); } } } /** * Decode and sample down a bitmap from a file input stream to the requested width and height. * * @param fileDescriptor The file descriptor to read from * @param reqWidth The requested width of the resulting bitmap * @param reqHeight The requested height of the resulting bitmap * @return A bitmap sampled down from the original with the same aspect ratio and dimensions * that are equal to or greater than the requested width and height */ public static Bitmap decodeSampledBitmapFromDescriptor(FileDescriptor fileDescriptor, int reqWidth, int reqHeight) { // First decode with inJustDecodeBounds=true to check dimensions final BitmapFactory.Options options = new BitmapFactory.Options(); options.inJustDecodeBounds = true; BitmapFactory.decodeFileDescriptor(fileDescriptor, null, options); // Calculate inSampleSize options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight); // Decode bitmap with inSampleSize set options.inJustDecodeBounds = false; return BitmapFactory.decodeFileDescriptor(fileDescriptor, null, options); } /** * Calculate an inSampleSize for use in a {@link BitmapFactory.Options} object when decoding * bitmaps using the decode* methods from {@link BitmapFactory}. This implementation calculates * the closest inSampleSize that will result in the final decoded bitmap having a width and * height equal to or larger than the requested width and height. This implementation does not * ensure a power of 2 is returned for inSampleSize which can be faster when decoding but * results in a larger bitmap which isn't as useful for caching purposes. * * @param options An options object with out* params already populated (run through a decode* * method with inJustDecodeBounds==true * @param reqWidth The requested width of the resulting bitmap * @param reqHeight The requested height of the resulting bitmap * @return The value to be used for inSampleSize */ public static int calculateInSampleSize(BitmapFactory.Options options, int reqWidth, int reqHeight) { // Raw height and width of image final int height = options.outHeight; final int width = options.outWidth; int inSampleSize = 1; if (height > reqHeight || width > reqWidth) { // Calculate ratios of height and width to requested height and width final int heightRatio = Math.round((float) height / (float) reqHeight); final int widthRatio = Math.round((float) width / (float) reqWidth); // Choose the smallest ratio as inSampleSize value, this will guarantee a final image // with both dimensions larger than or equal to the requested height and width. inSampleSize = heightRatio < widthRatio ? heightRatio : widthRatio; // This offers some additional logic in case the image has a strange // aspect ratio. For example, a panorama may have a much larger // width than height. In these cases the total pixels might still // end up being too large to fit comfortably in memory, so we should // be more aggressive with sample down the image (=larger inSampleSize). final float totalPixels = width * height; // Anything more than 2x the requested pixels we'll sample down further final float totalReqPixelsCap = reqWidth * reqHeight * 2; while (totalPixels / (inSampleSize * inSampleSize) > totalReqPixelsCap) { inSampleSize++; } } return inSampleSize; } /** * Get from memory cache. * * @param data Unique identifier for which item to get * @return The bitmap if found in cache, null otherwise */ public Bitmap getBitmapFromCache(String data) { if (mBitmapCache != null) { return mBitmapCache.get(data); } return null; } /** * Adds a bitmap to both memory and disk cache. * @param data Unique identifier for the bitmap to store * @param bitmap The bitmap to store */ public void addBitmapToCache(String data, Bitmap bitmap) { if (data == null || bitmap == null) { return; } // Add to memory cache if (mBitmapCache != null && mBitmapCache.get(data) == null) { mBitmapCache.put(data, bitmap); } } /** * Locate an existing instance of this Fragment or if not found, create and * add it using FragmentManager. * * @param fm The FragmentManager manager to use. * @return The existing instance of the Fragment or the new instance if just * created. */ public static RetainFragment findOrCreateRetainFragment(FragmentManager fm) { // Check to see if we have retained the worker fragment. RetainFragment mRetainFragment = (RetainFragment) fm.findFragmentByTag(TAG); // If not retained (or first time running), we need to create and add it. if (mRetainFragment == null) { mRetainFragment = new RetainFragment(); fm.beginTransaction().add(mRetainFragment, TAG).commit(); } return mRetainFragment; } /** * A simple non-UI Fragment that stores a single Object and is retained over configuration * changes. It will be used to retain the BitmapCache object. */ public static class RetainFragment extends Fragment { private Object mObject; /** * Empty constructor as per the Fragment documentation */ public RetainFragment() { } @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); // Make sure this Fragment is retained over a configuration change setRetainInstance(true); } /** * Store a single object in this Fragment. * * @param object The object to store */ public void saveObject(Object object) { mObject = object; } /** * Get the stored object. * * @return The stored object */ public Object getObject() { return mObject; } } }